The present invention comprises a new and distinct cultivar of Hydrangea plant known by the varietal name ‘Horstol’. The new variety was discovered in 2001 in a planned breeding program in Dresden, Germany. The purpose of the breeding program was to develop vigorous dark pink/red Hydrangeas. The new variety is the result of a cross between breeding selection 48-90/1 (female parent, unpatented) and ‘Rom’ (male parent, unpatented). The color of ‘Horstol’ is similar to 48-90/1, but ‘Horstol’ differs in growth habit and inflorescence diameter. The forcing time of ‘Horstol’ is similar to ‘Rom’, but ‘Horstol’ differs in color and growth habit. The new variety was first asexually reproduced in 2001 via propagation by cuttings in Germany. The new variety has been trial and field tested in Germany and has been found to retain its distinctive characteristics and remain true to type through successive propagations.
The following traits distinguish ‘Horstol’ as a new and distinct cultivar from other Hydrangea varieties known to the breeder:                1. Inflorescence size;        2. Stem quality;        3. Vigor;        4. Root system; and        5. Branching characteristics.        
‘Horstol’ is similar to another Hydrangea variety, ‘Merrits Supreme’ (unpatented), in color and because they are both mopheads. However, ‘Horstol’ differs from ‘Merrits Supreme’ in growth habit, branching characteristics and forcing time.